Update PHP Stan and fix some issues

Author: AydinHassan

composer.json

@@ -16,7 +16,7 @@
     "require-dev": {
         "phpunit/phpunit": "^8.0 | ^9.0",
         "squizlabs/php_codesniffer": "^3.2",
-        "phpstan/phpstan": "^0.12"
+        "phpstan/phpstan": "^1.2.0"
     },
     "require": {
         "php" : ">=7.1",

src/Style/DefaultStyle.php

@@ -8,9 +8,6 @@
 
 class DefaultStyle implements ItemStyle
 {
-    private const DEFAULT_STYLES = [
-    ];
-
     public function hasChangedFromDefaults() : bool
     {
         return true;

src/Util/ColourUtil.php

@@ -310,7 +310,7 @@ public static function map256To8(int $colourCode) : string
     public static function validateColour(Terminal $terminal, string $colour, string $fallback = null) : string
     {
         if (!ctype_digit($colour)) {
-            return static::validateColourName($colour);
+            return self::validateColourName($colour);
         }
 
         Assertion::between($colour, 0, 255, 'Invalid colour code');
@@ -320,7 +320,7 @@ public static function validateColour(Terminal $terminal, string $colour, string
         }
 
         if ($fallback !== null) {
-            return static::validateColourName($fallback);
+            return self::validateColourName($fallback);
         }
 
         return static::map256To8((int) $colour);